In severe sepsis, systemic inflammation induced by infection leads to vascular leakage, disseminated intravascular coagulation (DIC), microvascular thrombosis, multiple organ dysfunction, hemorrhage and circulatory collapse, resulting in high mortality. Although antibiotics and standard care regimens are helpful, they are ultimately ineffective for a significant percentage of patients. Despite years of intensive research, the only new drug approved by the FDA for treatment of severe sepsis is the recombinant activated protein C (APC, Xigris), which inhibits thrombin generation, prevents thrombosis and reduces inflammation. However, Xigris also causes hemorrhage, which outweighed its benefits and resulted in its withdrawal from the market. Thus, there is an urgent unmet need for new life-saving treatment of sepsis. In this application, we propose to develop a new drug for sepsis treatment, which potently inhibits both intravascular thrombosis and inflammation but does not cause bleeding. This innovative drug targets a novel integrin signaling mechanism recently discovered in the lab of Xiaoping Du, co-investigator of this application (Gong et al Science 2010, Shen et al, Nature 2013, Shen MBoC 2015), who demonstrated that integrin outside-in signaling requires direct interaction between the G protein subunit Ga13 and an ExE motif conserved in the cytoplasmic domain of several integrin b subunits (including b3 in platelets and b2 in leukocytes). Integrin-mediated cell adhesion and signaling are important in thrombosis and inflammation. Furthermore, inhibition of Ga13-integrin interaction abolishes outside-in signaling without affecting the ligand binding function of integrins important for hemostasis. Thus, we designed a selective peptide inhibitor of Ga13 binding ExE motif that potently inhibits occlusive intravascular thrombosis without causing excessive bleeding (Shen et al, Nature, 2013). Importantly, in preliminary studies using the CLP model, treatment of mice with the ExE motif peptide potently inhibits inflammation and thrombosis in septic mice, significantly reducing their mortality. We are thus submitting this Phase I SBIR grant with the following Specific Aims: (1) Pharmacologically characterize ExE motif peptide inhibitors for protective effects in CLP, endotoxin and bacteria induced sepsis models. (2) Determine the vascular safety of ExE motif peptides by evaluating their effects on vascular leakage and bleeding. (3) Based on the outcomes of Aims 1 and 2, develop novel high-loading peptide nanoparticles (HLPN) for efficiet in vivo delivery. The proposed work will provide the first steps in developing a novel drug that simultaneously targets two important pathological aspects of sepsis, thrombosis and excess inflammation, without impairing hemostasis and vascular integrity. This innovative strategy has the potential to significantly advance the therapeutic benefit of sepsis treatment. !